Gyro Horizon Indicator, British RAF Sperry Mark 1B Japanese as depicted in its Flight

as depicted in its Flight Manual (unfortunately the page showing the indicator does not photograph well)

25in diameter and ~4in deep

75in diameter and ~10in deep

The knob adjusts the accuracy of the reading by calibrating the instrument to the current barometric pressure as shown in the small window above center

or Mach Speed Indicator

Gyro Horizon Indicator, British RAF Sperry Mark 1B Japanese as depicted in its FlightHere is a British vacuum driven Gyro Horizon Indicator Sperry Mark 1B as used by aircraft of the Royal Air Force and British Fleet Air Arm during the 1940's and 1950's. This one has a manufacturing serial # incorporating "52", likely made in 1952. Measures 4. 5 inches diameter by 6. 5 inches long. The instrument looks terrific and would make a wonderful display piece, as long as you "Handle Like Eggs"!